[PEN-e posting] This report discusses the basic methodology of life-cycle assessments and compares several of the publicly available studies of GHG emissions data for Canadian oil sands crudes against each other and against those of other global reference crudes. As congressional concern over the environmental impacts of Canadian oil sands production may encompass both a broad understanding of the resource as well as a specific assessment of the proposed Keystone XL pipeline, the report surveys both the general scientific literature as well as the individual findings in the State Department’s 2011 Final EIS and 2013 Draft Supplementary EIS for the Keystone XL Project.